1. Field of the Invention
The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus having multiple DC loads which are effectively supplied with electric power from a single DC power supply.
2. Background and Related Art
Japanese Patent Unexamined Publication No. 63-95465 describes a conventional load power controller for a copying machine. The copying machine has two large power consuming AC loads: an exposure lamp and a fuser heater. Coordinating the operation of the exposure lamp and the fuser heater is important for consistent AC power distribution. For example, when the exposure lamp is lighting up, the AC power supply voltage varies depending upon whether the fuser heater is turned on or off. As a result of the voltage variation, the amount of light emitted from the exposure lamp varies, often causing copy irregularities (or density irregularities).
To avoid problems such as copy irregularities, the conventional load power controller provides staggered on-timings for the exposure lamp and the fuser heater so that these AC loads are not activated simultaneously. Accordingly, variations in the AC power supply voltage is minimized, thereby effectively eliminating the light amount variations of the exposure lamp (specifically, a density irregularities in copy images).
More recent copying machines contain many DC motors for driving certain components in the machine. For example, a copying machine may contain a paper feed motor, a drum motor, a transfer motor, a cleaning motor, a fuser motor, and a paper refeed motor for feeding paper from an intermediate tray. The copying machine may also contain a DC heater for heating a photosensitive drum.
A single DC power supply is generally used to provide DC power to the DC loads. The conventional load power controller for the AC loads described above has been proposed to control the DC power supplied to the multiple DC motors. Under this proposal, however, no consideration is given to the DC loads because the DC power supply, unlike the AC power supply, is free from voltage variation. When one of the DC loads is greatly increased, a safety circuit of the DC power supply restricts the output current therefrom, giving rise to a problem. With the current restricted, the DC motor requires more time to start up. No technical measure has been taken for such a problem.
Therefore, when multiple DC loads employed in conventional copying machines are employed, the current restriction from the DC power supply may result in unstable operation and delay in start up timings of the DC loads. Such a condition should be removed.
Accordingly, the present invention has a chief object to provide a power supply control device for controlling the power supplied to multiple DC loads from a single DC power supply.
Another conventional copying machine includes multiple drive devices, for driving corresponding DC motors, which are selectively driven according to a selected copy mode. However, in this copying machine, the order in which the drive devices are turned on according to copy modes has not been optimized for maximum operational efficiency. When switching from one copy mode to another, the first copy is remarkably slow due to the inefficient order of activating the drive devices. Thus, copying efficiency is impaired.
Accordingly, another object of the present invention is to provide a power supply control device for controlling the start-up timings of the DC motors in an efficient operating order according to copy modes.